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Nanoscale Infrared Spectroscopy: Improving the Spectral Range of the Photothermal Induced Resonance Technique
journal contribution
posted on 2013-02-19, 00:00 authored by Aaron
M. Katzenmeyer, Vladimir Aksyuk, Andrea CentronePhotothermal induced resonance (PTIR) is a new technique
which
combines the chemical specificity of infrared (IR) spectroscopy with
the lateral resolution of atomic force microscopy (AFM). PTIR requires
a pulsed tunable laser for sample excitation and an AFM tip to measure
the sample expansion induced by light absorption. The limited tunability
of commonly available laser sources constrains the application of
the PTIR technique to a portion of the IR spectrum. In this work,
a broadly tunable pulsed laser relying on a difference frequency generation
scheme in a GaSe crystal to emit light tunable from 1.55 μm
to 16 μm (from 6450 cm–1 to 625 cm–1) was interfaced with a commercial PTIR instrument. The result is
a materials characterization platform capable of chemical imaging,
in registry with atomic force images, with a spatial resolution that
notably surpasses the light diffraction limit throughout the entire
mid-IR spectral range. PTIR nanoscale spectra and images allow the
identification of compositionally and optically similar yet distinct
materials; organic, inorganic, and composite samples can be studied
with this nanoscale analog of infrared spectroscopy, suggesting broad
applicability. Additionally, we compare the results obtained with
the two tunable lasers, which have different pulse lengths, to experimentally
assess the recently developed theory of PTIR signal generation.
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Keywords
nanoscale analoglight tunabledifference frequency generation schemeSpectral Rangelight absorptionGaSe crystalchemical imaginglight diffraction limitPhotothermal Induced Resonance TechniquePhotothermalAFM tipPTIR signal generationlaser sourcessample excitationIR spectrumtunable laserspulse lengthstunable lasermaterials characterization platformPTIR nanoscale spectraforce microscopyPTIR instrumentchemical specificity1.55 μ mPTIR technique16 μ msample expansionforce images
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